Modern lubricating oil formulations are formulated to exacting specifications often set by original equipment manufacturers. To meet such specifications, various additives are used, together with base oil of lubricating viscosity. Depending on the application, a typical lubricating oil composition may contain dispersants, detergents, anti-oxidants, wear inhibitors, rust inhibitors, corrosion inhibitors, foam inhibitors, and friction modifiers just to name a few. Different applications will govern the type of additives that will go into a lubricating oil composition.
A functional fluid is a term which encompasses a variety of fluids including but not limited to tractor hydraulic fluids, power transmission fluids including automatic transmission fluids, continuously variable transmission fluids and manual transmission fluids, hydraulic fluids, including tractor hydraulic fluids, gear oils, power steering fluids, fluids used in wind turbines and fluids related to power train components. It should be noted that within each of these fluids such as, for example, automatic transmission fluids, there are a variety of different types of fluids due to the various transmissions having different designs which have led to the need for fluids of markedly different functional characteristics.
With respect to tractor hydraulic fluids, these fluids are all-purpose products used for all lubricant applications in a tractor except for lubricating the engine. Also included as a tractor hydraulic fluid for the purposes of this invention are so-called Super Tractor Oil Universal fluids or “STOU” fluids, which also lubricate the engine. These lubricating applications may include lubrication of gearboxes, power take-off and clutch(es), rear axles, reduction gears, wet brakes, and hydraulic accessories. The components included within a tractor fluid must be carefully chosen so that the final resulting fluid composition will provide all the necessary characteristics required in the different applications. Such characteristics may include the ability to provide proper frictional properties for preventing wet brake chatter of oil immersed brakes while simultaneously providing the ability to actuate wet brakes and provide power take-off (PTO) clutch performance. A tractor fluid must provide sufficient antiwear and extreme pressure properties as well as water tolerance/filterability capabilities. The extreme pressure (EP) properties of tractor fluids, important in gearing applications, may be demonstrated by the ability of the fluid to pass a spiral bevel test as well as a straight spur gear test. The tractor fluid may need to pass wet brake chatter tests while providing adequate wet brake capacity when used in oil immersed disk brakes which are comprised of a bronze, graphitic-compositions and asbestos. The tractor fluid may need to demonstrate its ability to provide friction retention for power shift transmission clutches such as those clutches which include graphitic and bronze clutches.
When the functional fluid is an automatic transmission fluid, the automatic transmission fluids must have enough friction for the clutch plates to transfer power. However, the friction coefficient of fluids has a tendency to decline due to the temperature effects as the fluid heats up during operation. It is important that the tractor hydraulic fluid or automatic transmission fluid maintain its high friction coefficient at elevated temperatures, otherwise brake systems or automatic transmissions may fail.
A need exists for an alternative organic wear inhibitor for use in tractor hydraulic fluids that maintains the protection of gears at slow speeds.
JP05-105895 teaches lubricating oil compositions for wet clutches and brakes used in power transmission units in among other uses in agricultural, construction, and other industrial machinery, containing 0.01-10 parts by weight of a C2-C14 aliphatic compound having two or more hydroxyl groups per 100 parts by weight of a base oil. In particular JP05-105895 teaches such oils are especially useful as transmission fluids. Glycerol is disclosed as such a C2-C14 aliphatic compound having two or more hydroxyl groups but is not exemplified.
Bayles, Jr. et al., U.S. Pat. No. 5,284,591, is directed to a multipurpose functional fluid which is comprised of a major amount of a hydrocarbon oil and a minor amount, sufficient to improve characteristics of the fluid of a novel additive. The additive is comprised of a calcium salt complex, a group II metal dithiophosphate salt, a borated epoxide, a carboxylic solubilizer and a sulfurized composition.
Stoffa et al., U.S. Pat. No. 5,635,459 is directed to a function fluid composition having improved gear performance which comprises an oil of lubricating viscosity, and added thereto (a) an alkali or alkaline earth metal salt complex in the form of borated and/or non-borated salts; (b) an EP/antiwear agent comprising a mixture of zinc salts of dialkylphosphorodithioic acid and 2-ehtylhexanoic acid heated with triphenyl phosphite or an olefin; and (c) a borated epoxide.